1. Field of the Invention
Embodiments of the invention relate to a liquid crystal display and a local dimming control method thereof capable of improving image quality.
2. Discussion of the Related Art
A range of application for liquid crystal displays has gradually widened because of its excellent characteristics such as light weight, thin profile, and low power consumption. The liquid crystal displays have been used in personal computers such as notebook PCs, office automation equipments, audio/video equipments, interior/outdoor advertising display devices, and the like. The liquid crystal displays display an image using a thin film transistor (TFT) as a switching element. A backlit liquid crystal display occupying most of the liquid crystal displays controls an electric field applied to a liquid crystal layer and modulates light coming from a backlight unit, thereby displaying an image.
The image quality of the liquid crystal display depends on its contrast characteristic. It is limited to improve the contrast characteristic using only a method for controlling a data voltage applied to the liquid crystal layer and modulating a light transmittance of the liquid crystal layer. As a solution thereto, a backlight dimming method has been proposed so as to improve the contrast characteristic. The backlight dimming method adjusts a luminance of a backlight unit depending on an image displayed on the liquid crystal display. The backlight dimming method includes a global dimming method for adjusting a luminance of the entire display surface of the liquid crystal display and a local dimming method for locally controlling a luminance of the display surface of the liquid crystal display. The global dimming method can improve a dynamic contrast ratio measured between two adjacent frames. The local dimming method can locally control the luminance of the display surface of the liquid crystal display within one frame period, thereby improving a static contrast ratio which is difficult to improve using the global dimming method.
As shown in FIG. 1, the local dimming method maps input data to a plurality of imaginary blocks BLK divided from a display surface of a liquid crystal display panel in a matrix form and obtains a representative value of the input data in each of the blocks BLK. The local dimming method adjusts a dimming value of each block BLK based on the representative value of each block BLK, thereby locally controlling a luminance of a backlight unit (i.e., light sources of the backlight unit). Further, the local dimming method multiplies the input data by a predetermined pixel gain value so as to compensate for a deficiency of the luminance of the backlight unit resulting from the adjustment of the dimming value of each block BLK, thereby compensating for the input data.
The pixel gain value is determined based on data required to allow a luminance obtained from a total amount of light (i.e., an amount of light in dimming) reaching a corresponding pixel in the local dimming using a dimming value of a block including the corresponding pixel to be equal to a luminance obtained from a total amount of light (i.e., an amount of light in non-dimming) reaching the corresponding pixel in non-local dimming. The pixel gain value is calculated by a ratio of the amount of light in the non-dimming to the amount of light in the dimming. The amount of light in the non-dimming indicates an amount of light reaching a corresponding pixel when all of the light sources are turned on at a maximum brightness and may be previously determined as a constant value for each pixel. As shown in FIG. 2, the amount of light in the dimming may be determined by a total amount of light reaching the corresponding pixel in an analysis area of size P×P surrounding a block including the corresponding pixel in the local dimming in a state where the block is positioned in the middle of the analysis area, where P indicates the number of blocks and is an odd number equal to or greater than 3.
However, as shown in FIG. 1, an operation for obtaining the pixel gain value has to be individually performed on all of the pixels and has to be performed in real-time. Therefore, the size of an algorithm of the operation for achieving the local dimming greatly increases.